JP6168454B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating apparatus that selects one heating coil from a plurality of heating coils, connects to a common resonant capacitor and a switching element, and heats an object to be heated by the selected heating coil. is there.

  A conventional induction heating apparatus has two heating coils, and an inverter circuit is configured by selectively connecting one of the two heating coils to a common resonance capacitor and switching element. There is a device for heating an object to be heated by supplying a high-frequency current to the inverter circuit. A switching relay is used as means for connecting one of the two heating coils to the resonant capacitor and the switching element. And in order to detect the abnormality of the contact of the switching relay, in the conventional induction heating apparatus, there is a thing provided with the circuit for detecting welding of a contact (for example, refer to patent documents 1).

  FIG. 4 is a block diagram showing a main circuit of a conventional induction heating apparatus described in Patent Document 1. As shown in FIG. The induction heating apparatus shown in FIG. 4 includes a first heating coil 50a, a second heating coil 50b, a first switching relay 51a, a second switching relay 51b, a first resonance capacitor 53a, and a second resonance capacitor. 53b, a switching element 54, an inverter drive circuit 55, a relay drive circuit 56, an oscillation voltage detection circuit 57, and a control unit 58.

  The oscillation voltage detection circuit 57 detects a high frequency voltage generated at both ends of the switching element 54. The control unit 58 detects whether the oscillation voltage detection circuit 57 detects zero V in the state where the relay drive circuit 56 outputs a signal for shutting off both the first switching relay 51a and the second switching relay 51b, or an inverter It is configured to detect whether a switching voltage at the time of oscillation of the circuit is detected and to detect an abnormality in the contact between the first switching relay 51a and the second switching relay 51b.

JP-A-9-140561

  However, in the conventional configuration, since the welding of the switching relay is detected every time the switching relay is switched, the inverter circuit is once operated after the switching relay is operated so as to temporarily disconnect all of the plurality of heating coils. Need to work. For this reason, there has been a problem that the number of switching of the switching relay is increased, and the life of the switching relay and the life of the device are shortened.

  The present invention solves the above-described conventional problem, and detects an abnormality of the contact of the switching relay without performing the switching operation of the switching relay as in the conventional configuration, thereby extending the life of the switching relay. An object of the present invention is to provide an induction heating apparatus capable of performing the above.

In order to solve the conventional problem, the induction heating device of the present invention is:
DC power supply,
A first heating coil;
A second heating coil;
A first connection terminal connected to one end of the first heating coil, a second connection terminal connected to one end of the second heating coil, and a common connected to the high potential side output terminal of the DC power supply A switching relay for connecting the common terminal to either the first connection terminal or the second connection terminal;
One end is connected to a connecting portion that connects the other end of the first heating coil and the other end of the second heating coil, and the other end is connected to the common terminal to connect the first heating coil or the second heating coil. A resonant capacitor that forms a resonant circuit with the two heating coils;
A switching element connected between the connection portion and a low-potential side output terminal of the DC power supply, and generating a resonance current in the resonance circuit;
A first voltage detection circuit for detecting a voltage at one end of the first heating coil;
A controller that drives the switching element to control the heating output of the first heating coil or the second heating coil to a predetermined value and controls switching of the switching relay;
The control unit is configured such that when a resonance current is generated in the resonance circuit, a detection voltage at one end of the first heating coil is an output voltage of the DC power source based on a detection result of the first voltage detection circuit. When it is detected that the voltage is within a first voltage range including a larger value, the common terminal is determined to be connected to the second connection terminal.

  In the induction heating apparatus of the present invention configured as described above, the control unit performs control so that the common terminal of the switching relay is connected to the first connection terminal, and performs on / off control of the switching element. When the voltage detection circuit detects that the voltage at one end of the first heating coil is within the first voltage range set larger than the output voltage of the DC power supply, that is, the first heating coil When it is detected that the voltage at one end is greater than the output voltage of the DC power supply, the voltage at one end of the first heating coil is in an open state, and the voltage at the other end of the second heating coil is greater than the output voltage of the DC power supply. It can be judged that it is large. For this reason, the control unit can determine that the common terminal of the switching relay is connected to the second connection terminal, and the resonance current is flowing through the second heating coil. That is, in the above state, the control unit controls the common terminal of the switching relay to be connected to the first connection terminal and performs on / off control of the switching element, so that the movable contact of the switching relay is in the second state. It can be detected that the terminal is welded to the connection terminal. Therefore, in the present invention, it is possible to reliably detect an abnormality in the contact of the switching relay without disconnecting all ends of the first heating coil and the second heating coil from the DC power supply.

  According to the present invention, in order to detect the abnormality of the contact of the switching relay, the abnormality of the contact of the switching relay can be detected without performing the switching operation of the switching relay specially, thereby extending the life of the switching relay, A reliable induction heating device having a long lifetime can be provided.

The block diagram which shows the main circuits of the induction heating apparatus of Embodiment 1 which concerns on this invention Main circuit diagram of first voltage detection circuit according to the first embodiment of the present invention The block diagram which shows the main circuits of the induction heating apparatus of Embodiment 2 which concerns on this invention Block diagram showing the main circuit of a conventional induction heating device

An induction heating apparatus according to a first aspect of the present invention is:
DC power supply,
A first heating coil;
A second heating coil;
A first connection terminal connected to one end of the first heating coil, a second connection terminal connected to one end of the second heating coil, and a common connected to the high potential side output terminal of the DC power supply A switching relay for connecting the common terminal to either the first connection terminal or the second connection terminal;
One end is connected to a connecting portion that connects the other end of the first heating coil and the other end of the second heating coil, and the other end is connected to the common terminal to connect the first heating coil or the second heating coil. A resonant capacitor that forms a resonant circuit with the two heating coils;
A switching element connected between the connection portion and a low-potential side output terminal of the DC power supply, and generating a resonance current in the resonance circuit;
A first voltage detection circuit for detecting a voltage at one end of the first heating coil;
A controller that drives the switching element to control the heating output of the first heating coil or the second heating coil to a predetermined value and controls switching of the switching relay;
The control unit is configured such that when a resonance current is generated in the resonance circuit, a detection voltage at one end of the first heating coil is an output voltage of the DC power source based on a detection result of the first voltage detection circuit. When it is detected that the voltage is within a first voltage range including a larger value, the common terminal is determined to be connected to the second connection terminal.

  In the configuration according to the first aspect of the present invention configured as described above, when the common terminal is not connected to the first connection terminal, the resonance current does not flow through the first heating coil. The voltage detection circuit detects a voltage applied to a connection portion between the other end of the first heating coil and the other end of the second heating coil. When the control unit detects that the voltage at one end of the first heating coil is within the first voltage range including a value larger than the output voltage of the DC power source based on the detection result of the first voltage detection circuit, That is, when it is detected that the voltage at one end of the first heating coil is greater than the output voltage of the DC power supply, one end of the first heating coil is open and the voltage at the connection is greater than the output voltage of the DC power supply. Judge. For this reason, a control part determines with the resonant current flowing into the 2nd heating coil. As described above, the control unit determines that the common terminal is not connected to the first connection terminal but is connected to the second connection terminal based on the detection result of the first voltage detection circuit. Can do. Therefore, when the control unit detects the connection state as described above in a state where the common terminal of the switching relay is controlled to be connected to the first connection terminal and the switching element is on / off controlled, the switching relay It can be determined that the movable contact is in a welded state with the second connection terminal.

  In the induction heating apparatus according to the second aspect of the present invention, the control unit according to the first aspect detects the first voltage detection circuit when a resonance current is generated in the resonance circuit. Based on the result, when it is detected that the detection voltage at one end of the first heating coil is the same as the output voltage of the DC power supply, it is determined that the common terminal is connected to the first connection terminal Has been.

  When a resonance current is generated in the resonance circuit, the voltage at one end of the first heating coil is the case where the common terminal is connected to the first connection terminal and the case where the common terminal is connected to the second connection terminal. And the voltage is different. When the common terminal is connected to the first connection terminal, it has the same voltage as the output terminal on the high potential side of the DC power supply. When the common terminal is connected to the second connection terminal, That is, the voltage generated between the second heating coil terminals is added to the voltage at the output terminal on the high potential side of the DC power supply. The control unit controls the common terminal of the switching relay to be connected to the first connection terminal, and controls the switching element to be turned on and off so that the common terminal is normally connected to the first connection terminal. It is possible to accurately determine that the connection terminal 2 is not connected.

  As described above, even when the control unit according to the second aspect of the present invention is controlled so as to connect the common terminal of the switching relay to either the first connection terminal or the second connection terminal, Without newly performing the switching operation of the switching relay, it can be reliably confirmed whether or not the switching relay is operating normally as instructed.

  In the induction heating apparatus according to the third aspect of the present invention, when the control unit according to the first aspect or the second aspect generates a resonance current in the resonance circuit, Based on the detection result of the voltage detection circuit, when it is detected that the detection voltage at one end of the first heating coil is equal to or lower than a threshold having a value smaller than the output voltage of the DC power supply, the switching relay operates normally. It is configured to determine that it is not.

  The control unit according to the third aspect of the present invention configured as described above performs control so that the common terminal of the switching relay is connected to the first connection terminal, and the switching element is on / off controlled. It can be determined that the terminal is normally connected to the first connection terminal and not connected to the second connection terminal.

  In the induction heating apparatus according to the fourth aspect of the present invention, when the control unit according to the first aspect or the second aspect generates a resonance current in the resonance circuit, When the voltage detection circuit detects a zero voltage, it is configured to determine that neither the first connection terminal nor the second connection terminal is connected to the common terminal.

  In the fourth aspect of the present invention configured as described above, the first voltage detection circuit is not connected to the common terminal unless both the first connection terminal and the second connection terminal are connected to the coil. A voltage of almost zero V is detected. In both cases where the first connection terminal is connected to the common terminal and in the state where the second connection terminal is connected to the common terminal, the first voltage detection circuit outputs the output of the DC power supply. Detects a voltage higher than the voltage. Therefore, according to the present invention, when the first voltage detection circuit detects a voltage of substantially zero V, it can be determined that neither the first connection terminal nor the second connection terminal is connected to the common terminal. For example, in the configuration of the fourth aspect, a switching operation of the switching relay is newly added that foreign matter such as dust is caught between the contacts of the switching relay and the heating coil to be operated is not connected. Can be detected.

An induction heating apparatus according to a fifth aspect of the present invention is
DC power supply,
A first heating coil;
A second heating coil;
A first connection terminal connected to one end of the first heating coil, a second connection terminal connected to one end of the second heating coil, and a common connected to the high potential side output terminal of the DC power supply A switching relay for connecting the common terminal to either the first connection terminal or the second connection terminal;
One end is connected to a connecting portion that connects the other end of the first heating coil and the other end of the second heating coil, and the other end is connected to the common terminal to connect the first heating coil or the second heating coil. A resonant capacitor that forms a resonant circuit with the two heating coils;
A switching element connected between the connection portion and a low-potential side output terminal of the DC power supply, and generating a resonance current in the resonance circuit;
A second voltage detection circuit for detecting a voltage of the connecting portion connecting the other end of the first heating coil and the other end of the second heating coil;
A controller that drives the switching element to control the heating output of the first heating coil or the second heating coil to a predetermined value and controls switching of the switching relay;
The control unit is configured such that when a resonance current is generated in the resonance circuit with a predetermined heating output, a detection voltage of the connection unit is within a second voltage range based on a detection result of the second voltage detection circuit. When it is detected that the common terminal is connected to the second connection terminal,
The second voltage range does not include the voltage value of the connection portion that occurs when the resonance current is generated in the first heating coil with a predetermined heating output, and the second heating coil has a predetermined value in the second heating coil. It is set so as to include the voltage value of the connecting portion that is generated when the resonance current is generated with the heating output.

  In the configuration according to the fifth aspect of the present invention configured as described above, the common terminal is connected to the first connection terminal and a resonance current is passed through the first heating coil, and the common terminal is connected to the second connection terminal. The second voltage detection circuit detects a different high-frequency voltage in the case where a resonance current is passed through the second heating coil by connecting to the connection terminal. The control unit can determine which heating coil is operating according to the voltage value detected by the second voltage detection circuit.

  In the induction heating apparatus according to the sixth aspect of the present invention, when the control unit according to the fifth aspect generates a resonance current in the resonance circuit with a predetermined heating output, Based on the detection result of the voltage detection circuit, when the detection voltage of the connection portion detects the voltage value of the connection portion that occurs when the resonance current is generated in the first heating coil with the predetermined heating output The common terminal is configured to be determined to be connected to the first connection terminal.

  As described above, even when the control unit according to the sixth aspect of the present invention is controlled to connect the common terminal of the switching relay to either the first connection terminal or the second connection terminal, Without newly performing the switching operation of the switching relay, it can be reliably confirmed whether or not the switching relay is operating normally as instructed.

  In the induction heating apparatus according to the seventh aspect of the present invention, when the control unit according to the fifth aspect generates a resonance current in the resonance circuit with a predetermined heating output, When the voltage detection circuit detects zero voltage, it is determined that neither the first connection terminal nor the second connection terminal is connected to the common terminal.

  As described above, in the control unit according to the seventh aspect of the present invention, when the second voltage detection circuit detects a zero voltage, both the first connection terminal and the second connection terminal are common terminals. By configuring so as not to be connected, for example, foreign matter such as dust is caught between the contacts of the switching relay, and one of the first heating coil and the second heating coil that attempts to flow a resonance current is used. It can be detected that the heating coil is not connected and is not connected to the other heating coil.

  Hereinafter, an induction heating apparatus will be described as an embodiment according to the present invention with reference to the accompanying drawings. The induction heating device of the present invention is not limited to the configuration of the induction heating device described in the following embodiment, and is based on a technical idea equivalent to the technical idea described in the following embodiment. The induction heating apparatus comprised is comprised.

(Embodiment 1)
FIG. 1 is a block diagram showing a main circuit of the induction heating apparatus according to the first embodiment of the present invention.

  In FIG. 1, a DC power source 1 includes a diode bridge 2 constituting a full-wave rectifier as a rectifier, a choke coil 3 having one end connected to the high potential side output end of the diode bridge 2, and the other end of the choke coil 3. And the smoothing capacitor 4 connected between the low-potential side output terminal of the diode bridge 2. The AC power source 5 is connected to the input terminal of the DC power source 1. In the first embodiment, for the sake of explanation, the AC power source 5 is an AC 100 V having a frequency of 50 Hz or 60 Hz, which is a commercial power source in Japan. The AC power supply 5 is not limited to the configuration of the first embodiment. The DC power supply 1 forms a DC voltage obtained by rectifying and smoothing the AC voltage of the AC power supply 5, and outputs the formed DC voltage to both ends of the smoothing capacitor 4. The output terminal 1 a on the high potential side of the DC power supply 1 is connected to the high potential side terminal of the smoothing capacitor 4. The output terminal 1 b on the low potential side of the DC power supply 1 is connected to the low potential output terminal of the diode bridge 2 and the low potential terminal of the smoothing capacitor 4.

  The input terminal 6 a on the high potential side of the inverter circuit 6 is connected to the output terminal 1 a of the DC power supply 1, and the input terminal 6 b on the low potential side connected to the common potential of the inverter circuit 6 is the output terminal 1 b of the DC power supply 1. Connected to. When the inverter circuit 6 operates, the DC power supply 1 supplies the inverter circuit 6 with a pulsating DC voltage on which a ripple having a frequency twice that of the AC power supply 5 is superimposed.

  The inverter circuit 6 includes a first heating coil 9 and a second heating coil 10. The inverter circuit 6 also generates a resonance current in a resonance capacitor 7 that forms a resonance circuit that resonates with either the first heating coil 9 or the second heating coil 10 to generate a resonance current. For this reason, the switching element 8 is connected to one end 7a of the resonance capacitor 7 and one end 8a on the high potential side. When a resonance current flows through the resonance circuit, a high frequency magnetic field is generated in the first heating coil 9 or the second heating coil 10, and an object to be heated is moved by the first heating coil 9 or the second heating coil 10. Induction heating.

  The switching relay 11 includes three terminals: a common terminal 12, a first connection terminal 13, and a second connection terminal 14. The switching relay 11 moves the movable contact when a drive signal is sent to a drive electromagnetic coil (not shown), and selectively selects the common terminal 12 as the first connection terminal 13 or the second connection terminal. 14 is connected to either one of them. The common terminal 12 is connected to the input terminal 6 a of the inverter circuit 6.

  One end 9 a of the first heating coil 9 is connected to the first connection terminal 13 of the switching relay 11. The other end 9 b of the first heating coil 9 is connected to one end 7 a of the resonance capacitor 7. One end 10 a of the second heating coil 10 is connected to the second connection terminal 14 of the switching relay 11. The other end 10 b of the second heating coil 10 is connected to the one end 7 a of the resonance capacitor 7 at the connection portion 16 together with the other end 9 b of the first heating coil 9.

  In the first voltage detection circuit 17, the input terminal 17 b having a common potential is connected to the input terminal 6 b on the low potential side of the inverter circuit 6, and the input terminal 17 a on the high potential side is connected to one end 9 a of the first heating coil 9. It is connected. The first voltage detection circuit 17 detects a voltage VA between the one end 9a of the first heating coil 9 and the common potential of the inverter circuit 6 (hereinafter simply referred to as voltage VA), and the detection result is detected. The data is output from the output terminal 17c and the output terminal 17d to the control unit 18.

  The control unit 18 is configured by a circuit including a microcomputer, and performs control to send a drive signal to an electromagnetic coil (not shown) for driving the switching relay 11 to switch the movable contact of the switching relay 11. Thereby, the control unit 18 selectively connects the common terminal 12 to either the first connection terminal 13 or the second connection terminal 14. Thereafter, the control unit 18 sends a drive signal to the switching element 8 to cause the inverter circuit 6 to oscillate. The input current detection unit 32 detects the input current of the DC power supply 1 corresponding to the heating output of the first heating coil 9 or the second heating coil 10. The magnitude of this input current substantially matches the magnitude of the input current of the inverter circuit 6. Thus, the input current of the inverter circuit 6 is monitored, and the control unit 18 controls the heating output of the induction heating device to a predetermined value.

  FIG. 2 is a circuit diagram showing the main part of the first voltage detection circuit 17 according to the first embodiment of the present invention.

  In the first voltage detection circuit 17, the input terminal 17b on the low potential side has a common potential. The input end 17 b is connected to the common potential of the inverter circuit 6, and the high potential side input end 17 a is connected to one end 9 a of the first heating coil 9. Therefore, the first voltage detection circuit 17 detects the voltage VA at the one end 9 a of the first heating coil 9. The first voltage detection circuit 17 includes a voltage dividing circuit 21, a peak hold circuit 22, a reference voltage generation circuit 26, and a comparison circuit 29.

  The voltage dividing circuit 21 includes a series circuit of a resistor 19 and a resistor 20 that divides the voltage VA. The peak hold circuit 22 includes a collector resistor 22a, a transistor 22c, an emitter resistor 22b, and a capacitor 22d. The peak hold circuit 22 holds a peak voltage of the divided voltage obtained by dividing the voltage VA by the voltage dividing circuit 21 and outputs an output voltage VB (hereinafter referred to as a voltage between the common potential of the first voltage detection circuit 17). Simply referred to as the output voltage VB). Similarly, voltages VC, VD, V1, and V2, which will be described later, indicate voltages between the common potential of the first voltage detection circuit 17. The reference voltage generation circuit 26 includes a series circuit of a resistor 23, a resistor 24, and a resistor 25 connected between the control power supply V and a common potential. In the reference voltage generation circuit 26, the potential at the connection point between the resistor 23 and the resistor 24 generates the reference voltage V1, and the potential at the connection point between the resistor 24 and the resistor 25 generates the reference voltage V2 (V1> V2).

  The comparison circuit 29 includes a first comparator 27 and a second comparator 28. The first comparator 27 compares the output voltage VB of the peak hold circuit 22 with the first reference voltage V1 generated by the reference voltage generation circuit 26. When VB> V1, the HIGH signal is output from the output terminal 17c. Output (HIGH output). On the other hand, when VB ≦ V1, a LOW signal is output (LOW output). The second comparator 28 compares the output voltage VB of the peak hold circuit 22 with the second reference voltage V2 generated by the reference voltage generation circuit 26. If VB> V2, the HIGH signal is output from the output terminal 17c. Output. On the other hand, when VB ≦ V2, a LOW signal is output. The comparison circuit 29 outputs the outputs of the two comparators 27 and 28 to the control unit 18.

  In the first embodiment, the voltage dividing ratio of the voltage dividing circuit 21 is set so as to divide the voltage VA at the one end 9a of the first heating coil 9 to approximately 1/100. Note that the voltage dividing ratio of the voltage dividing circuit 21 is not limited to the configuration of the first embodiment, and may be set as appropriate so as to satisfy the electrical ratings of the components constituting the first voltage detection circuit 17.

  The operation and action of the induction heating apparatus according to Embodiment 1 configured as described above will be described below.

  As shown in FIG. 1, in the switching relay 11, it is assumed that the common terminal 12 and the first connection terminal 13 are connected. In this state, one end 9a of the first heating coil 9 has the same voltage as the output voltage VC (about 141 V) of the DC power supply 1. Therefore, regardless of whether or not the inverter circuit 6 performs an oscillation operation, the voltage VA input to the first voltage detection circuit 17 is a direct current whose peak voltage is substantially equal to the output voltage VC of the direct current power source 1. The output voltage VB of the peak hold circuit 22 is VB≈VC / 100 = 1.4V.

  Next, although not illustrated, in the switching relay 11, it is assumed that the common terminal 12 and the second connection terminal 14 are connected. In this state, the voltage VA input to the first voltage detection circuit 17 is the same as the voltage VD at the other end 10 b of the second heating coil 10 because no resonance voltage is generated at both ends of the second heating coil 10. become.

  In a state where the inverter circuit 6 is not oscillating, the voltage VD at the other end 10 b of the second heating coil 10 is equal to the output voltage VC of the DC power supply 1.

  When the inverter circuit 6 is oscillated, the voltage VD at the other end 10 b of the second heating coil 10 is obtained by adding the high-frequency voltage generated at both ends of the second heating coil 10 to the output voltage VC of the DC power supply 1. It becomes the value. The output voltage VC of the DC power source 1 is a pulsating voltage obtained by rectifying the AC power source 5, and in the first embodiment, the peak voltage is about 141 V and the frequency is 120 Hz or 100 Hz. Due to the switching operation of the switching element 8 at a high frequency (for example, about 30 kHz), the second heating coil 10 and the resonance capacitor 7 resonate, and a high frequency voltage is generated at both ends of the second heating coil 10. For example, the voltage VD at the other end 10b of the second heating coil 10 in the inverter circuit 6 is a high frequency voltage having a peak voltage of about 650V and a frequency of about 33 kHz.

  As described above, the voltage VA input by the first voltage detection circuit 17 is equal to the output voltage VC of the DC power source 1 when the inverter circuit 6 is not oscillated, and when the oscillation operation is performed. Becomes equal to the voltage VD which is a high frequency voltage.

  The output voltage VB of the peak hold circuit 22 is VB≈VC / 100 = 1.4 V when the oscillation of the inverter circuit 6 is stopped, and VB≈when the inverter circuit 6 is oscillating. VD / 100 = 6.5V.

  Furthermore, although not illustrated, it is assumed that the common terminal 12 of the switching relay 11 is not connected to either the first connection terminal 13 or the second connection terminal 14. In this state, since the output voltage VC of the DC power source 1 is not applied to the inverter circuit 6, the voltage VA input to the first voltage detection circuit 17 is zero V, and the output voltage VB of the peak hold circuit 22 is also zero. V.

  As described above, the output voltage VB of the peak hold circuit 22 shows different values corresponding to the state of the movable contact of the switching relay 11. The comparison circuit 29 receives the output voltage VB of the peak hold circuit 22 and can identify the state of the movable contact of the switching relay 11. In the first embodiment, the first reference voltage V1 and the second reference voltage generated by the reference voltage generation circuit 26 in the first voltage detection circuit 17 for comparison with the output voltage VB of the peak hold circuit 22 are used. The voltage values of V2 are set to V1 = 4.0V and V2 = 0.6V, respectively. However, these set values are merely examples, and the present invention is not limited to these numerical values, and is set as appropriate according to the specifications of the circuit configuration.

  In addition, in the induction heating apparatus of Embodiment 1 which concerns on this invention, the said 1st reference voltage V1 and the 2nd reference voltage V2 are the criteria of a contact state as a threshold value, respectively. The first reference voltage V1 or higher is set as the first voltage range.

  Next, the contact state detection operation of the switching relay 11 in the induction heating operation of the first embodiment will be described in the order of the connection state of the switching relay 11 described above.

[Common terminal 12 and first connection terminal 13 are connected]
First, in the switching relay 11, when the common terminal 12 and the first connection terminal 13 are in the connected state, as described above, the inverter circuit 6 is in an oscillation operation state and in an oscillation stop state. In either state, the output voltage VB of the peak hold circuit 22 is VB≈1.4V. For this reason, the output of the first comparator 27 of the comparison circuit 29 is a LOW output (LOW signal output), and the output of the second comparator 28 is a HIGH output (HIGH signal output).

[Common terminal 12 and second connection terminal 14 are connected]
Next, when the common terminal 12 and the second connection terminal 14 of the switching relay 11 are in the connected state, the output voltage VB of the peak hold circuit 22 is as described above when the inverter circuit 6 is not oscillated. Is VB≈1.4V. As a result, the output of the first comparator 27 of the comparison circuit 29 is a LOW output, and the output of the second comparator 28 is a HIGH output. In a state where the inverter circuit 6 is performing the oscillation operation, the output voltage VB of the peak hold circuit 22 is VB≈6.5. For this reason, in a state where the inverter circuit 6 is oscillating, both the output of the first comparator 27 and the output of the second comparator 28 of the comparison circuit 29 are HIGH outputs.

[The common terminal 12 is not connected]
Further, when the common terminal 12 of the switching relay 11 is not connected to either the first connection terminal 13 or the second connection terminal 14, the inverter circuit 6 does not oscillate and the peak The output voltage VB of the hold circuit 22 becomes zero V. Further, the output of the first comparator 27 and the output of the second comparator 28 of the comparison circuit 29 are both LOW outputs.

  Therefore, in the state where the inverter circuit 6 has stopped oscillating, the control unit 18 outputs both the output of the first comparator 27 and the output of the second comparator 28 which are input signals from the first voltage detection circuit 17 as LOW output. In this case, for example, foreign matter such as dust is sandwiched between the movable contact of the switching relay 11 and the contact of the first connection terminal 13 or the second connection terminal 14, and the common terminal 12 is connected to the first connection terminal 13 or the first connection terminal 13. It is possible to detect that the connection terminal 14 is not connected to any of the two connection terminals 14.

[Control unit 18 connects common terminal 12 and first connection terminal 13]
The control unit 18 generates a high-frequency magnetic field from the first heating coil 9 and heats the object to be heated so as to send a command signal for connecting the common terminal 12 of the switching relay 11 and the first connection terminal 13 to each other. When the inverter circuit 6 is oscillated by outputting, the connection state of the switching relay 11 can be detected by the input signal (HIGH signal / LOW signal) from the first voltage detection circuit 17 as follows.

  When the control unit 18 causes the common terminal 12 and the first connection terminal 13 to be connected and causes the inverter circuit 6 to oscillate, the output of the first comparator 27 is the LOW output, and the second comparator 28 When the output is a HIGH output, it can be detected that the common terminal 12 of the switching relay 11 is normally connected to the first connection terminal 13, and the movable contact of the switching relay 11 is normal. Can be detected.

  Further, when the command signal for connecting the common terminal 12 and the first connection terminal 13 of the switching relay 11 is output and the inverter circuit 6 is oscillated, the output of the first comparator 27 and the second When both the outputs of the comparators 28 are HIGH outputs, it can be detected that the common terminal 12 of the switching relay 11 is connected to the second connection terminal 14. Therefore, it can be detected that the movable contact of the switching relay 11 is welded to the second connection terminal 14.

[Control unit 18 connects common terminal 12 and second connection terminal 14]
The control unit 18 generates a high-frequency magnetic field from the second heating coil 10 to heat the object to be heated, and outputs a command signal for connecting the common terminal 12 of the switching relay 11 and the second connection terminal 14 to each other. When the inverter circuit 6 is oscillated by outputting, the connection state of the switching relay 11 can be detected by the input signal (HIGH signal / LOW signal) from the first voltage detection circuit 17 as follows.

  When the control unit 18 causes the common terminal 12 and the second connection terminal 14 to be in a connected state and causes the inverter circuit 6 to oscillate, both the output of the first comparator 27 and the output of the second comparator 28 are HIGH outputs. In this case, it can be detected that the common terminal 12 of the switching relay 11 is normally connected to the second connection terminal 14, and the contact of the switching relay 11 can be detected to be normal.

  Further, when a command signal for connecting the common terminal 12 and the second connection terminal 14 of the switching relay 11 is output and the inverter circuit 6 is oscillated, the output of the first comparator 27 is a LOW output. Yes, when the output of the second comparator 28 is a HIGH output, it can be detected that the common terminal 12 of the switching relay 11 is connected to the first connection terminal 13, and the movable contact of the switching relay 11. Can be detected as being welded to the first connection terminal 13.

  As described above, the induction heating apparatus according to the first embodiment includes the first heating coil 9, the second heating coil 10, the switching relay 11, the resonant capacitor 7, the switching element 8, and the first voltage. A detection circuit 17 and a control unit 18 are provided.

  In the induction heating device according to the first embodiment, the switching relay 11 includes a first connection terminal 13 connected to one end 9 a of the first heating coil 9 and a first connection terminal 13 a connected to one end 10 a of the second heating coil 10. 2 connection terminals 14 and a common terminal 12 connected to the output terminal 1a on the high potential side of the DC power supply 1. The switching relay 11 is configured to be switched by a movable contact so that the common terminal 12 is connected to either the first connection terminal 13 or the second connection terminal 14.

  The resonance capacitor 7 has one end connected to the connection portion 16 between the other end 9 b of the first heating coil 9 and the other end 10 b of the second heating coil 10, and the other end connected to the output terminal on the high potential side of the DC power supply 1. Connected to form a resonance circuit with the first heating coil 9 or the second heating coil 10.

  The switching element 8 is connected between the connection part 16 of the other end 9b of the first heating coil 9 and the other end 10b of the second heating coil 10 and the output terminal on the low potential side of the DC power supply 1. Then, a resonance current is generated in the resonance circuit by turning on and off the switching element 8. The first voltage detection circuit 17 is configured to detect the voltage at one end of the first heating coil 9 and output the detection result to the control unit 18. The control unit 18 controls on / off of the switching element 8 so that the heating output of the first heating coil 9 or the second heating coil 10 becomes a predetermined value, and also controls switching of the movable contact of the switching relay 11. . And the control part 18 can detect the contact state of the switching relay 11 as mentioned above based on the detection result of the 1st voltage detection circuit 17, when the resonance current has generate | occur | produced in the resonance circuit.

  In the first embodiment, the control unit 18 is within a first voltage range in which the voltage (VA) at one end of the first heating coil 9 is set larger than the output voltage (for example, about 141 V) of the DC power supply 1 (for example, , It is determined that the common terminal 12 is connected to the second connection terminal 14 when it is detected that the voltage is at the first reference voltage V1 (approximately 4.0 V or higher).

  In the configuration of the first embodiment, when the first connection terminal 13 is not connected to the common terminal 12 of the switching relay 11, no resonance current flows through the first heating coil 9. For this reason, the 1st voltage detection circuit 17 detects the voltage VD added to the connection part 16 of the other end 9b of a 1st heating coil, and the other end 10b of a 2nd heating coil. When the common terminal 12 is connected to the second connection terminal 14 and a resonance current is flowing through the second heating coil 10, the voltage VD of the connection portion 16 is higher than the output voltage VC of the DC power supply 1.

  Therefore, the control unit 18 is within the first voltage range in which the voltage VA at one end of the first heating coil 9 is set larger than the output voltage VC of the DC power source 1 based on the detection result of the first voltage detection circuit 17. Is detected, that is, when it is detected that the voltage VA at one end of the first heating coil 9 is larger than the output voltage VC of the DC power supply 1, one end of the first heating coil 9 is open and connected. It can be determined that the voltage VD of the unit 16 is greater than the output voltage VC of the DC power supply 1. As a result, in the induction heating apparatus of the first embodiment, it can be determined that the resonance current is flowing in the second heating coil 10. Accordingly, the control unit 18 can determine that the common terminal 12 is connected to the second connection terminal 14.

  For example, the control unit 18 outputs a command signal so as to connect the common terminal 12 of the switching relay 11 to the first connection terminal 13 and controls the switching element 8 to be turned on / off. When it is detected that VD is greater than the output voltage VC of the DC power supply 1, it can be determined that the movable contact of the switching relay 11 is in a welded state with the second connection terminal 14.

  In the first embodiment, the control unit 18 determines that the voltage detected by the first voltage detection circuit 17 is the same as the output voltage VC of the DC power supply 1 when a resonance current is generated in the resonance circuit. When detected, it is determined that the common terminal 12 is connected to the first connection terminal 13.

  When a resonance current is generated in the resonance circuit, the voltage VA at one end 9a of the first heating coil 9 is the same as when the common terminal 12 is connected to the first connection terminal 13 and the second connection terminal 14. The voltage differs depending on whether it is connected to. When the common terminal 12 is connected to the first connection terminal 13, the voltage VC is the same as that of the output terminal 1 a on the high potential side of the DC power supply 1, and the common terminal 12 is connected to the second connection terminal 14. If it is, the voltage VD is the same voltage as the connection portion 16, that is, the voltage VD obtained by adding the voltage at both ends of the second heating coil 10 to the voltage VC at the output terminal 1 a on the high potential side of the DC power supply 1.

  The control unit 18 further determines that the voltage VA at the one end 9a of the first heating coil 9 is based on the detection result of the first voltage detection circuit 17 when the resonance current is generated in the resonance circuit. When it is detected that the output voltage is the same as the output voltage VC, it can be determined that the common terminal 12 is connected to the first connection terminal 13 and a resonance current is flowing through the first heating coil 9.

  For example, when the control unit 18 controls the common terminal 12 of the switching relay 11 to be connected to the first connection terminal 13 and controls the switching element 8 to be turned on and off, the control unit 18 controls the one end 9a of the first heating coil. If the voltage VA is the output voltage VC of the DC power source 1, it can be determined that the common terminal 12 is normally connected to the first connection terminal 13.

  As described above, the control unit 18 generates a resonance current in the resonance circuit and detects the voltage VA at the one end 9a of the first heating coil 9, so that the common terminal 12 of the switching relay 11 is connected to any connection terminal. Even if connected, it is possible to confirm whether the switching relay 11 is operating normally as instructed by the control unit 18 without newly performing the switching operation of the switching relay.

  The control unit 18 determines whether or not the voltage VA at the one end 9a of the first heating coil 9 is the output voltage VC of the DC power supply 1, and the common terminal 12 is normal to the first connection terminal 13. And detecting that the voltage VA at one end 9a of the first heating coil 9 is within a first voltage range set larger than the output voltage VC of the DC power supply 1. Thus, it may be determined whether or not the switching relay 11 is normally performing the switching operation by using only one of the methods for determining that the common terminal 12 is connected to the second connection terminal 14. .

  In the first embodiment, when the first voltage detection circuit 17 detects a zero voltage, the control unit 18 connects both the first connection terminal 13 and the second connection terminal 14 to the common terminal 12. Judge that it is not. Thereby, the contact of the switching relay 11 can be obtained without switching the contact of the switching relay 11 to a specific state, that is, without newly adding a switching operation of the switching relay 11 and in a state where no resonance current is generated in the resonance circuit. It can be detected that foreign matter such as dust is caught between the first heating coil 9 and the second heating coil 10 to be operated by the control unit 18 so that a resonance current cannot be generated.

  In the first embodiment, the first voltage detection circuit 17 is configured to detect the peak voltage of the voltage VA at the one end 9 a of the first heating coil 9, so that the common terminal 12 includes the first voltage detection circuit 17. The difference in input voltage VA, which is different between the case where the connection terminal 13 is connected and the case where the second connection terminal 14 is connected, is accurately grasped, and the identification sensitivity at the time of determination is increased, so that the difference between the two Can be reliably detected.

  In the first embodiment, the reference voltage in the first voltage detection circuit 17 is set to two voltages V1 and V2, and both the contact opening due to foreign matter adhering to the switching relay 11 and the welding of the contacts are detected. However, the reference voltage may be only V1, and only contact welding may be detected.

  In addition, the switching relay 11 uses a relay that has two contacts with one relay and can be switched so that the common terminal is connected to one of the contacts. The same effect can be obtained by using two relays for switching the terminal and its contact point between connection and non-connection and connecting the common terminals of the two relays.

  Further, the switching relay 11 in the first embodiment is configured to perform the switching operation for the two heating coils 9 and 10, but is configured to be connectable to three or more heating coils, and one of the heating coils is selected. Thus, even when the inverter circuit 6 is connected, the number of reference voltages generated by the reference voltage generation circuit 26 and the number of comparators (comparators) in the comparison circuit 29 are matched with the number of heating coils. Can do. That is, when the number of heating coils is A, the number of reference voltages is A, and the number of comparators in the comparison circuit is A. With this configuration, the control unit generates a peak voltage of the high-frequency voltage generated by the resonance of the heating coil and the resonance capacitor based on the output signal from the first voltage detection circuit and applied to the switching element. This makes it possible to detect which heating coil is connected to the common terminal of the switching relay.

  Note that the functions of the reference voltage generation circuit 26 and the comparison circuit 29 may be included in a microcomputer provided in the control unit 18, and the first voltage detection circuit 17 uses at least the voltage VA at one end of the heating coil 9 or 10. A corresponding voltage or signal may be output to the control unit 18.

(Embodiment 2)
Hereinafter, the induction heating apparatus of Embodiment 2 which concerns on this invention is demonstrated, referring FIG. FIG. 3 is a block diagram showing a main circuit of the induction heating apparatus according to the second embodiment of the present invention. In the description of the second embodiment, components having the same functions as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 3, the second voltage detection circuit 30 in the second embodiment has the same configuration as the first voltage detection circuit 17 shown in FIG. 2, but the input terminal 17 a is the first. The second embodiment is different from the first embodiment in that it is connected to a connecting portion 16 between the other end 9b of the heating coil 9 and the other end 10b of the second heating coil 10 and detects the voltage VD.

  In the second embodiment, when the resonance current is supplied to the first heating coil 9 to obtain a predetermined heating output (for example, 1200 W), the voltage VD of the connecting portion 16 is the second voltage VD. A resonance current is supplied to the heating coil 10 to obtain a predetermined heating output (for example, 1200 W), so that the first heating coil 9 and the second heating coil 9 are larger than the voltage VD of the connection portion 16 when the predetermined heating output is obtained. This is different from the first embodiment in that the specification of the heating coil 10 is determined.

  The control unit 31 in the second embodiment controls the switching relay 11 to connect the common terminal 12 to the first connection terminal 13 (first heating coil 9), and resonates with the resonance circuit with a predetermined heating output. When the current is generated, based on the detection result of the second voltage detection circuit 30, the common terminal 12 is connected to the second connection terminal 14 when the voltage VD of the connection unit 16 is within the second voltage range. This embodiment is different from the first embodiment in that it is determined that the connection is made. Here, the second voltage range does not include the voltage value of the connection portion 16 generated when the first heating coil 9 generates a resonance current with a predetermined heating output, and the second heating coil 10. Is a range including the voltage value of the connection portion 16 generated when a resonance current is generated with a predetermined heating output.

  About the induction heating apparatus of Embodiment 2 comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  When the common terminal 12 of the switching relay 11 is not connected to either the first connection terminal 13 or the second connection terminal 14, the voltage VD input to the second voltage detection circuit 30 is zero V. The output voltage VB of the peak hold circuit 22 is also zero V.

  In the switching relay 11, when the common terminal 12 and the first connection terminal 13 are connected (see FIG. 3), when the control unit 18 stops the oscillation of the inverter circuit 6, The voltage VD input to the voltage detection circuit 30 is the same voltage as the output voltage VC of the DC power supply 1.

  When the inverter circuit 6 oscillates in this connected state (see FIG. 3), the voltage VD input to the second voltage detection circuit 30 is applied to the resonance circuit of the first heating coil 9 and the resonance capacitor 7. A voltage generated at both ends of the first heating coil 9 by the generated resonance current becomes a high frequency voltage added to the output voltage VC of the DC power supply 1. The control unit 31 detects the input current detected by the input current detection unit 32 and controls the switching element 8 so that the heating output of the first heating coil 9 becomes a predetermined value, for example, 1200 W. At this time, the voltage VD input to the second voltage detection circuit 30 is, for example, a high-frequency voltage having a peak voltage of about 750 V and a frequency of about 30 kHz.

  Therefore, the output voltage VB of the peak hold circuit 22 is VB≈VC / 100 = 1.4 V when the oscillation of the inverter circuit 6 is stopped, and VB when the inverter circuit 6 is oscillating. ≈VD / 100 = 7.5V.

  On the other hand, when the switching relay 11 is connected to the common terminal 12 and the second connection terminal 14 (second heating coil 10) and the control unit 18 stops the oscillation of the inverter circuit 6, The voltage VD of the connection portion 16 between the other end 9b of the heating coil 9 and the other end 10b of the second heating coil 10 is the same as the output voltage VC of the DC power supply 1 that is the same as the voltage VC of the output end 1a of the DC power supply 1. become.

  In this connection state, when the inverter circuit 6 is oscillated, the voltage VD of the connection portion 16 is generated by the resonance current generated in the resonance circuit of the second heating coil 10 and the resonance capacitor 7. The voltage generated at both ends is a high-frequency voltage applied to the output voltage VC of the DC power supply 1. In the second embodiment, this high-frequency voltage is a high-frequency voltage having a peak voltage of about 650 V and a frequency of about 33 kHz.

  Therefore, the waveform of the output voltage VB of the peak hold circuit 22 is VB≈VC / 100 = 1.4 V when the inverter circuit 6 is not oscillating, and when the inverter circuit 6 is oscillating. VB≈VD / 100 = 6.5V.

  In the second embodiment, the voltage values of the first reference voltage V1 and the second reference voltage V2 generated by the reference voltage generation circuit 26 in the second voltage detection circuit 30 are V1 = 7.0V, V2 respectively. = 0.6V.

  In the induction heating apparatus according to the second embodiment of the present invention, the first reference voltage V1 and the second reference voltage V2 are used as threshold values for determining the contact state.

  In a state where the common terminal 12 of the switching relay 11 is not connected to either the first connection terminal 13 or the second connection terminal 14, VD = 0V, so that the first comparator 27 of the comparison circuit 29 Both the output and the output of the second comparator 28 are LOW outputs.

  When the common terminal 12 of the switching relay 11 is connected to the first connection terminal 13, the output voltage VB of the peak hold circuit 22 is VB≈when the inverter circuit 6 stops oscillating. VC / 100 = 1.4V. Conversely, when the inverter circuit 6 is oscillating, VB≈VD / 100 = 7.5V. Therefore, the output of the first comparator 27 of the comparison circuit 29 in a state where the oscillation of the inverter circuit 6 is stopped is a LOW output, and the output of the second comparator 28 is a HIGH output. On the contrary, the output of the first comparator 27 of the comparison circuit 29 in the state where the inverter circuit 6 is performing the oscillation operation is a HIGH output, and the output of the second comparator 28 is a HIGH output.

  On the other hand, when the common terminal 12 of the switching relay 11 is connected to the second connection terminal 14, the output voltage VB of the peak hold circuit 22 is VB≈when the inverter circuit 6 stops oscillating. VC / 100 = 1.4V. Conversely, when the inverter circuit 6 is oscillating, VB≈VD / 100 = 6.5V. Therefore, the output of the first comparator 27 of the comparison circuit 29 when the inverter circuit 6 is not oscillating is a LOW output, and the output of the second comparator 28 is a HIGH output. Conversely, the output of the first comparator 27 of the comparison circuit 29 in a state where the inverter circuit 6 is oscillating is a LOW output, and the output of the second comparator 28 is a HIGH output.

  Therefore, in the state where the inverter circuit 6 has stopped oscillating, the control unit 18 determines that the input signal from the second voltage detection circuit 30 is that the output of the first comparator 27 and the output of the second comparator 28 are both LOW output. In this case, it can be detected that foreign matter such as dust is caught between the common terminal 12 and the first connection terminal 13 or the contact between the common terminal 12 and the second connection terminal 14 of the switching relay 11 and cannot be connected. it can.

  The control unit 18 also connects the common terminal 12 of the switching relay 11 to the first connection terminal 13 in order to generate a high-frequency magnetic field from the first heating coil 9 and heat the object to be heated. When the output of the first comparator 27 is a HIGH output and the output of the second comparator 28 is a HIGH output in response to an input signal from the second voltage detection circuit 30 with the circuit 6 oscillating. It can be detected that the contact of the switching relay 11 is normally connected to the first connection terminal 13. As a result, the control unit 18 can detect that the contact of the switching relay 11 is normal.

  In this connection state, when the output of the first comparator 27 in the input signal from the second voltage detection circuit 30 is a LOW output and the output of the second comparator 28 is a HIGH output, the contact of the switching relay 11 Can be detected as being connected to the second connection terminal 14. Therefore, the control unit 31 can detect that the movable contact of the switching relay 11 is welded to the second connection terminal 14.

  On the other hand, in order to generate a high-frequency magnetic field from the second heating coil 10 and heat the object to be heated, the control unit 18 connects the common terminal 12 of the switching relay 11 to the second connection terminal 14 and connects the inverter When the circuit 6 oscillates, switching is performed when the output of the first comparator 27 is LOW output and the output of the second comparator 28 is HIGH output according to the input signal from the second voltage detection circuit 30. It can be detected that the contact of the relay 11 is normally connected to the second connection terminal 14, and the contact of the switching relay 11 can be detected to be normal.

  In this connection state, when both the output of the first comparator 27 and the output of the second comparator 28 in the input signal from the second voltage detection circuit 30 are HIGH outputs, the common terminal 12 of the switching relay 11 is It can be detected that the terminal is connected to one connection terminal 13. Therefore, the control unit 31 can detect that the movable contact of the switching relay 11 is welded to the first connection terminal 13.

  As described above, the second embodiment includes the second voltage detection circuit 30 that detects the voltage VD of the connection portion 16 between the other end 9b of the first heating coil and the other end 10b of the second heating coil. The control unit 31 controls the switching relay 11 so as to connect the common terminal 12 to the first connection terminal 13 and generates a resonance current in the resonance circuit with a predetermined heating output. Based on the detection result of the detection circuit 30, the voltage VD of the connection part 16 does not include the voltage value of the connection part 16 generated when the first heating coil 9 generates a resonance current with a predetermined heating output, and When the second heating coil 10 is within the second voltage range including the voltage value of the connection portion 16 generated when a resonance current is generated with a predetermined heating output, the common terminal 12 is the second connection terminal. Connected to 14 It is configured to determine.

  In the specific configuration of the second embodiment, the second voltage range refers to the voltage of the connection portion 16 (for example, 7) generated when the first heating coil 9 generates a resonance current with a predetermined heating output. .5V) and a voltage range including the voltage of the connection portion 16 (for example, 6.5V) generated when the second heating coil 10 generates a resonance current with a predetermined heating output. say. Therefore, in the second embodiment, when the voltage VD of the connection unit 16 is in the voltage range equal to or higher than the first reference voltage (for example, V1 = 7.0 V), the first heating coil 9 is set to the predetermined value. The resonance current is generated with the heating output of. In addition, the voltage VD of the connection portion 16 is less than the first reference voltage V1 (for example, V1 = 7.0V) and is within a voltage range equal to or higher than the second reference voltage V2 (for example, V2 = 0.6V) ( In the second voltage range, the second heating coil 10 is in a state of generating a resonance current with a predetermined heating output. In the state where the inverter circuit 6 stops oscillating, the voltage (VD≈1.4V) of the connection portion 16 is less than the first reference voltage V1 (for example, V1 = 7.0V), and the second reference voltage V2 (For example, V2 = 0.6V) or more.

  The induction heating apparatus according to the second embodiment is configured as described above so that the common terminal 12 is connected to the first connection terminal 13 and a resonance current is passed through the first heating coil 9. 12 is connected to the second connection terminal 14 and a resonance current is caused to flow through the second heating coil 10, the second voltage detection circuit 30 detects different high-frequency voltages. The control unit 31 can determine which heating coil is operating according to the voltage value detected by the second voltage detection circuit 30.

  Further, in the second embodiment, when the second voltage detection circuit 30 detects zero voltage, the control unit 31 connects both the first connection terminal 13 and the second connection terminal 14 to the common terminal 12. It is comprised so that it may determine that there is no. For this reason, in the induction heating device according to the second embodiment, foreign matter such as dust is caught between the contacts of the switching relay 11, and the first heating coil 9 or the second heating coil 10 that attempts to flow the resonance current is not connected. It is the structure which can detect that it is.

  In the second embodiment, since the second voltage detection circuit 30 is configured to detect the peak voltage of the voltage VD of the connection portion 16, the common terminal 12 is connected to the first connection terminal 13 and the second connection voltage. The voltage difference applied to the connection portion 16 can be reliably detected at a voltage value that differs depending on which of the connection terminals 14 is connected.

  In the second embodiment, the comparison voltage in the second voltage detection circuit 30 is set to two voltages of voltage VA and voltage VB, and both contact opening due to foreign matter adhering to the switching relay 11 and contact welding are detected. Although the configuration is adopted, the comparison voltage may be only the voltage VA so that only the welding of the contacts can be detected.

  In addition, the switching relay 11 uses a relay that has two contacts with one relay and can be switched so that the common terminal is connected to one of the contacts. The same effect can be obtained by using two relays for switching the terminal and its contact point between connection and non-connection and connecting the common terminals of the two relays.

  Further, the switching relay 11 in the second embodiment is configured to perform the switching operation for the two heating coils 9 and 10, but is configured to be connectable to three or more heating coils, and one of the heating coils is selected. And even when connected to the inverter circuit 6, it is possible to cope with this by matching the number of reference voltages generated by the reference voltage generation circuit and the number of comparators (comparators) of the comparison circuit with the number of heating coils. . That is, when the number of heating coils is A, the number of reference voltages is A, and the number of comparators in the comparison circuit is A. With this configuration, the control unit generates a peak voltage of the high-frequency voltage generated by the resonance of the heating coil and the resonance capacitor based on the output signal from the first voltage detection circuit and applied to the switching element. This makes it possible to detect which heating coil is connected to the common terminal of the switching relay.

  Note that the functions of the reference voltage generation circuit 26 and the comparison circuit 29 may be included in a microcomputer provided in the control unit 31, and the second voltage detection circuit 30 has at least a voltage corresponding to the voltage VD of the connection unit 16 or What is necessary is just to output a signal to the control part 31.

  As described above, in the induction heating device of the present invention, the control unit drives the switching relay so as to connect the common terminal connected to the DC power source and the first connection terminal. And a connection state of the second connection terminal connected to one end of the second heating coil can be detected. Therefore, the switching relay can be switched without performing an additional switching operation of the switching relay such that the connection state is detected after the first connection terminal and the second connection terminal are disconnected from each other as in the prior art. The connection state can be detected. As a result, according to the present invention, it is possible to extend the life of the switching relay, and thus to provide an induction heating device with a long life and high reliability.

  The induction heating apparatus of the present invention has a plurality of heating coils, and supplies various heating devices such as rice cookers and electromagnetic induction heating cookers that supply high-frequency power to each heating coil in a time series from one inverter circuit. Applicable.

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Diode bridge 3 Choke coil 4 Smoothing capacitor 5 AC power supply 6 Inverter circuit 7 Resonance capacitor 8 Switching element 9 1st heating coil 10 2nd heating coil 11 Switching relay 12 Common terminal 13 1st connection terminal 14 Second connection terminal 16 Connection unit 17 First voltage detection circuit 18 Control unit 21 Voltage division circuit 22 Peak hold circuit 26 Reference voltage generation circuit 27 First comparator 28 Second comparator 30 Second voltage detection circuit 31 Control 32 Input current detector

Claims (7)

DC power supply,
A first heating coil;
A second heating coil;
A first connection terminal connected to one end of the first heating coil, a second connection terminal connected to one end of the second heating coil, and a common connected to the high potential side output terminal of the DC power supply A switching relay for connecting the common terminal to either the first connection terminal or the second connection terminal;
One end is connected to a connecting portion that connects the other end of the first heating coil and the other end of the second heating coil, and the other end is connected to the common terminal to connect the first heating coil or the second heating coil. A resonant capacitor that forms a resonant circuit with the two heating coils;
A switching element connected between the connection portion and a low-potential side output terminal of the DC power supply, and generating a resonance current in the resonance circuit;
A first voltage detection circuit for detecting a voltage at one end of the first heating coil;
A controller that drives the switching element to control the heating output of the first heating coil or the second heating coil to a predetermined value and controls switching of the switching relay;
The control unit is configured such that when a resonance current is generated in the resonance circuit, a detection voltage at one end of the first heating coil is an output voltage of the DC power source based on a detection result of the first voltage detection circuit. An induction heating apparatus configured to determine that the common terminal is connected to the second connection terminal when it is detected that the voltage is within a first voltage range including a larger value.   The control unit is configured such that when a resonance current is generated in the resonance circuit, a detection voltage at one end of the first heating coil is an output voltage of the DC power source based on a detection result of the first voltage detection circuit. The induction heating device according to claim 1, wherein when the same is detected, the common terminal is determined to be connected to the first connection terminal.   The control unit is configured such that when a resonance current is generated in the resonance circuit, a detection voltage at one end of the first heating coil is an output voltage of the DC power source based on a detection result of the first voltage detection circuit. 3. The induction heating apparatus configured according to claim 1, wherein when it is detected that the value is equal to or less than a threshold having a smaller value, the switching relay is determined not to operate normally.   When the resonance voltage is generated in the resonance circuit and the first voltage detection circuit detects a zero voltage, the control unit detects both the first connection terminal and the second connection terminal. The induction heating device according to claim 1, wherein the induction heating device is configured to determine that the common terminal is not connected. DC power supply,
A first heating coil;
A second heating coil;
A first connection terminal connected to one end of the first heating coil, a second connection terminal connected to one end of the second heating coil, and a common connected to the high potential side output terminal of the DC power supply A switching relay for connecting the common terminal to either the first connection terminal or the second connection terminal;
One end is connected to a connecting portion that connects the other end of the first heating coil and the other end of the second heating coil, and the other end is connected to the common terminal to connect the first heating coil or the second heating coil. A resonant capacitor that forms a resonant circuit with the two heating coils;
A switching element connected between the connection portion and a low-potential side output terminal of the DC power supply, and generating a resonance current in the resonance circuit;
A second voltage detection circuit for detecting a voltage of the connecting portion connecting the other end of the first heating coil and the other end of the second heating coil;
A controller that drives the switching element to control the heating output of the first heating coil or the second heating coil to a predetermined value and controls switching of the switching relay;
The control unit is configured such that when a resonance current is generated in the resonance circuit with a predetermined heating output, a detection voltage of the connection unit is within a second voltage range based on a detection result of the second voltage detection circuit. When it is detected that the common terminal is connected to the second connection terminal,
The second voltage range does not include the voltage value of the connection portion that occurs when the resonance current is generated in the first heating coil with a predetermined heating output, and the second heating coil has a predetermined value in the second heating coil. An induction heating device that is set to include a voltage value of the connecting portion that is generated when the resonance current is generated with a heating output of.   The control unit is configured such that when a resonance current is generated in the resonance circuit with a predetermined heating output, a detection voltage of the connection unit is set based on a detection result of the second voltage detection circuit. And detecting the voltage value of the connecting portion generated when the resonance current is generated with the predetermined heating output, the common terminal is determined to be connected to the first connecting terminal. Item 6. The induction heating apparatus according to Item 5.   When the second voltage detection circuit detects a zero voltage when a resonance current is generated in the resonance circuit with a predetermined heating output, the control unit detects the first connection terminal and the second The induction heating device according to claim 5, wherein neither of the connection terminals is determined to be connected to the common terminal.

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